Eco-terrorism is the pursuit of terrorist tactics against civilian populations and property to promote ecological political causes. Terrorism per se is organized politically motivated violence against civilians in violation of the Geneva Conventions and which is intended in inciting terror among the population in order to motivate political change. Ecological groups engaged in eco-terrorism have ranged in the modern era between The Unabomber lone wolf, to Greenpeace, Sea Shepherd, Earth First!, People for the Ethical Treatment of Animals, Earth Liberation Front, and Animal Liberation Front.
Greenpeace began as an antinuclear protest organization in the late 1960's that was slowly suborned by radical leftists, but quickly expanded into a broader environmentalist organization. They have protested nuclear weapons testing, nuclear power plant construction and operations, whaling, dolphin-unsafe tuna fishing and other unsustainable industrial fishing practices, and hydropower, solar power, and other seemingly eco-friendly renewable energy projects, but while confrontational and obstructionary, frequently putting themselves in harms way to block actions they sought to end, like subsea nuclear weapons tests, they have rarely put the general public at risk.
The FBI has determined that terrorism began to be adopted by eco-terrorists in 1977 when Earth First! started spiking old growth trees in the Pacific Northwest of the United States in order to deter loggers from cutting old growth trees due to the risks of equipment damage and human injury and loss of life that frequently results from such damage. Members of Earth First! were then prosecuted for starting to bomb loggers vehicles, after one protester was killed in their own vehicle by a premature explosion.
The Earth Liberation Front or ELF was founded by members of Earth First! who believed that group was not effective enough at forcing change and that more radical action was necessary. The Animal Liberation Front or ALF was formed by animal rights activists that frequently overlapped with ELF and they have shared similar web hosts and spokespersons. Where ELF would attack logging and ski resorts, GMO labs and farm crops, ALF would attack labs conducting animal testing and farming for non-food purposes, like mink and fox farms. ELF/ALF were the first new domestic terrorist groups identified by the FBI since the end of the Civil Rights Era.
ALF has significant membership crossover with People for the Ethical Treatment of Animals, which also engages in actions against animal industries and consumers of animal products, but typically with a bias shown. For instance, PETA and ALF members will frequently target female models and celebrities wearing fur, leather, or animal-tested makeup for public harassment and even attacks with balloons or buckets of blood (particularly on fur in order to ruin its value), but will not visit the same treatment on, say, biker gangs. They will harass hunters alone in the woods (for which there are significant penalties in most states), but not cattle ranchers.
The ELF/ALF organization has been blamed for many millions of dollars in property damage and injury to a number of people, but no actual deaths until they backed away from violent action after 9/11.